In Vitro Inhibitory Activity of Andrographolide Combined with Polymyxins against Carbapenem-Resistant Enterobacterales

Objective To investigate the antibacterial effect of Andrographolide Combined with Polymyxins on Carbapenem-resistant Enterobacterales(CRE) Methods A total of 166 clinical CRE isolates were collected from Shaoxing People’s Hospital between January 2020 and December 2024. The minimum inhibitory concentration (MIC) of Andrographolide alone and in combination with Polymyxins against CRE was determined via the broth microdilution method. The fractional inhibitory concentration (FIC) index was calculated to evaluate the combined antibacterial efficacy against polymyxin-resistant CRE isolates. Bacterial motility assay was performed to detect the inhibitory effect of Andrographolide on flagella-mediated motility of polymyxin-resistant strains. Results Among the 166 CRE isolates, the Polymyxin resistance rate was 7.2%. The MIC range of Polymyxins was 0.03–64 μg/mL, while the MIC of Andrographolide ranged from 32 to 512 mg/mL. In the bacterial swimming experiment, 8.43% of bacteria were inhibited at a concentration of 1/8 MIC, 20.48% at a concentration of 1/4 MIC, 61.45% at a concentration of 1/2 MIC, and 87.95% at a concentration of 1.0MIC.Combination therapy exerted synergistic effects against 5 strains and additive effects against another 4 strains. Conclusion Andrographolide can reduce the MIC of Polymyxins, and the combination presents favorable antibacterial efficacy against polymyxin-resistant CRE.